Wear-resistant high-strength roll-formed components

ABSTRACT

A method of forming a component having a cross-section with a bend radius includes providing a work-piece blank from press-hardened steel (PHS). The method also includes austenitizing the work-piece blank in a furnace via heating the strip of sheet metal to achieve therein an austenite microstructure, including soaking the work-piece blank for a predetermined amount of time. The method additionally includes quenching the austenitized work-piece blank to achieve therein a martensitic matrix microstructure with dispersed chromium-enriched carbide. The method also includes roll-forming the austenitized and quenched work-piece blank to generate the cross-section and the bend radius. The method may further include locally heating the bend radius area during the roll-forming of the cross-section to reduce an amount of chromium-enriched carbide in the martensitic matrix microstructure inside the bend radius area relative to the microstructure outside the bend, and thereby generating the component having high strength, ductility, and wear resistance.

CLAIM OF PRIORITY AND CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Chinese Application Serial No.CN202210084483.2 filed Jan. 25, 2022, the entire content of which isincorporated by reference in its entirety.

INTRODUCTION

The present disclosure relates to system and a method for production ofwear-resistant high-strength roll-formed components.

Metal forming is a metalworking process for producing metal parts andobjects through mechanical deformation, where the workpiece is reshapedwithout adding or removing material. Metal forming operates on thematerials science principle of plastic deformation, where the physicalshape of the metal workpiece is permanently deformed. Roll-forming orrolling is a metal forming process in which metal stock is passedthrough one or more pairs of rolls to shape the workpiece and impart adesired mechanical property to the finished component without reducingthe metal's thickness.

Roll-forming involves continuous bending of a long strip of sheet metal(typically coiled steel) into a desired cross-section. The metal stripgenerally passes through multiple sets of rolls mounted on consecutivestands, each set performing an incremental part of the bend, until thedesired cross-section (profile) is obtained. Roll-forming is well suitedfor producing constant-profile parts with long lengths and in largequantities. Roll stands holding pairs of rolls are typically groupedtogether into rolling mills capable of quickly processing metal,typically steel, into products such as structural steel beams, barstock, and rails.

SUMMARY

A method of forming a component having a cross-section with a bendcharacterized by a bend radius includes providing a work-piece blankfrom press-hardened steel (PHS). The method also includes austenitizingthe work-piece blank in a furnace via heating the strip of sheet metalto achieve therein an austenite microstructure, including soaking thework-piece blank for a predetermined amount of time. The methodadditionally includes quenching the austenitized work-piece blank toachieve therein a martensitic matrix microstructure with dispersedcarbide. The method also includes roll-forming the austenitized andquenched work-piece blank via at least one set of rolls to generate thecross-section having the bend radius.

The method may further include locally heating an area of the bendradius during the roll-forming of the cross-section to reduce an amountof the chromium-enriched carbide in the martensitic matrixmicrostructure inside the bend radius area relative to the martensiticmatrix microstructure outside the bend radius. Locally heating the areaof the bend radius during the roll-forming of the quenching theaustenitized work-piece blank cross-section will thus generate thecomponent having high strength, ductility, and wear resistance.

According to the method, the predetermined amount of time may be in arange of 1-1000 seconds, and may further be in a range of 200-500seconds.

According to the method, the quenching may be performed at a rategreater than 10° C. per second.

The cross-section may have a 1:1 ratio of material thickness to the bendradius, i.e., the bend radius may be equal to the thickness of thework-piece blank without cracks or tears.

According to the method, locally heating the austenitized and quenchedwork-piece blank may be performed via a laser, a microwave, or aninfrared device during the roll-forming.

The PHS of the work-piece blank may include carbon (C) may be in a rangeof 0.05-0.45% by weight, manganese (Mn) in a range of 0-4.5% by weight,chromium (Cr) in a range of 0.5-6% by weight, and silicon (Si) in arange of 0.5-2.5% by weight.

The amount of chromium in the chromium-enriched carbide may be greaterthan 2% by weight.

Particles of the chromium-enriched carbide may have a diameter in arange of 5 nm-1.5 μm.

The martensitic matrix microstructure with dispersed carbide may includemartensite (with optional austenite/ferrite martensite at less than 10%by volume and optional ferrite at less than 5% by volume) at greaterthan 85% by volume, and chromium-enriched carbide in a range of 0.2-10%by volume.

The austenitized and quenched strip of PHS may have tensile strength ina range of 1000-2000 MPa.

The above features and advantages, and other features and advantages ofthe present disclosure, will be readily apparent from the followingdetailed description of the embodiment(s) and best mode(s) for carryingout the described disclosure when taken in connection with theaccompanying drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective illustration of roll-forming andlocalized heating a press-hardened steel (PHS) work-piece blank togenerate a structural component having a small radius bend, according tothe disclosure.

FIG. 2 is a schematic close-up illustration of a cross-section of thestructural component roll-formed from the work-piece blank as shown inFIG. 1 , according to the disclosure.

FIG. 3 is an illustration of a martensitic matrix microstructure withdispersed chromium-enriched carbide of the structural componentroll-formed from the PHS work-piece blank.

FIG. 4A is a data plot depicting stress vs strain comparison of PHSwithout carbide and PHS enriched with carbide.

FIG. 4B is a data plot depicting wear resistance comparison of PHSwithout carbide and PHS enriched with carbide.

FIG. 4C is a data plot depicting impact toughness comparison of PHSwithout carbide and PHS enriched with carbide.

FIG. 5 is a flow chart illustrating a method of roll-forming thestructural component from the PHS work-piece blank shown in FIGS. 1-4 .

FIG. 6 is a data plot depicting austenitizing temperature versus timefor the structural component formed from the PHS work-piece blank havingthe martensitic matrix microstructure with dispersed chromium-enrichedcarbide shown in FIG. 3 , according to the disclosure.

DETAILED DESCRIPTION

Referring to the drawings in which like elements are identified withidentical numerals throughout, FIG. 1 illustrates, in detail, processingand forming of a work-piece blank 10. Such work-piece blanks 10 arefrequently used in manufacturing processes, such as metal stamping orroll-forming, to produce specifically shaped high strength components.Typically, such components are formed from work-piece blanks 10. Eachwork-piece blank 10 is typically a pre-cut piece of formable material,for example sheet metal, such as cold rolled steel.

Specifically, the formable material may be a press-hardened steel (PHS)selected for the subject work-piece blank 10 used in manufacture of astructural component 12. The component 12 is a high strength and wearresistant part having high ductility or fracture toughness. Thestructural component 12 may, for example, be an automotive body framerail shown in FIG. 1 or a cross-member (not shown). PHS is ahigh-strength steel typically delivered in rolls or coils of varioussizes for blanking, austenitizing, and additional processing. Generally,austenitization and quenching is a hardening process used on iron-basedmetals to promote better mechanical properties of the material. Thepurpose of austenitizing steel and other ferrous alloys is to soften thematerials for forming them into the required shape, while the purpose ofquenching is to provide strength and resistance to the material.

The temperature at which steel and other ferrous alloys are heated abovetheir critical temperatures is called the austenitizing temperature. Theaustenitizing temperature range varies for different grades of carbon,alloys, and tool steels. After the metal is heated into the austeniteregion, it is then quenched in a heat extraction medium. Generally,press hardening, a.k.a., hot stamping or hot press forming, allows PHSsteels to be formed into complex shapes not commonly possible withregular cold stamping operations. However, PHS is typically not used forroll-formed part due to likelihood of material splits and tears,especially in tight radii of the component cross-sections generated byforming rolls.

The work-piece blank 10 is generally cut from a strip or coil 14 of PHSdescribed above to be subsequently austenitized, quenched, androll-formed to produce the structural component 12. The unformedwork-piece blank 10 may be initially austenitized in a furnace 16 (shownin FIG. 1 ). To achieve a martensitic matrix microstructure which willbe described in detail below, austenitization of the work-piece blank 10may be performed at a predetermined temperature, above austenitizingtemperature Ac3 (shown in FIG. 6 ), with the work-piece blank 10 soakedat the specific temperature for a predetermined amount of time. Theresultant tensile strength of the austenitized and quenched work-pieceblank 10 may be in a range of 1000-2000 MPa (shown in FIG. 4A).

Following austenitization, the work-piece blank 10 may be quenched at arate of greater than 10° C. per second and transferred to a system ofrolls 18 (shown in FIG. 1 ) having at least one set of rolls 18A. Asshown, the system of rolls 18 may include multiple sets of rolls mountedon consecutive stands, with each set of rolls generating an incrementalpart of the component 12. The austenitized and quenched work-piece blank10 may be locally heated during roll-forming via a heating device 20,such as a laser, a microwave, or an infrared source, in the area wherethe rolls 18A come into contact with the blank material. In a system 18employing multiple rolls, each respective roll 18A may be paired with acorresponding heating device 20 to locally heat the area of thework-piece blank 10 undergoing deformation. Localized heating isintended to improve roll-formability of the work-piece blank 10,especially when generated from high-strength steel, such as austenitizedand quenched PHS. The local heating thus enables the PHS work-pieceblank 10 to be formed into the component 12 having the desired shapealong with high strength, ductility, and wear resistance.

As used to manufacture the component 12, PHS includes carbon (C) in arange of 0.05-0.45% by weight, manganese (Mn) in a range of 0-4.5% byweight, chromium (Cr) in a range of 0.5-6% by weight, and silicon (Si)in a range of 0.5-2.5% by weight. The structural component 12 has adesired final shape or contour 12A (shown in FIG. 1 ) and across-section or profile 12B with one or more bends 22 characterized bya radius R (shown in FIG. 2 ). The component 12 material has amartensitic matrix microstructure 24 with dispersed chromium-enrichedcarbide 26, shown in FIG. 3 . While PHS without carbide has similartensile properties to PHS enriched with carbide (stress vs straincomparison shown in FIG. 4A), and specifically with chromium-enrichedcarbide, PHS enriched with carbide will provide comparatively higherstrength and wear resistance (wear resistance comparison shown in FIG.4B and impact toughness comparison shown in FIG. 4C).

The martensitic matrix microstructure 24 with dispersedchromium-enriched carbide 26 may specifically include martensite (withoptional austenite at less than 10⁰/by volume and optional ferrite atless than 5% by volume) at greater than 85% by volume, and further atgreater than 90% by volume. The martensitic matrix microstructure 24with dispersed chromium-enriched carbide 26 may additionally includechromium-enriched carbide in a range of 0.2-10% by volume, austenite atless than 10% by volume, and ferrite at less than 5% by volume. Themartensite in the martensitic matrix microstructure 24 may also,optionally, include austenite/ferrite martensite. The amount of chromiumin the chromium-enriched carbide 26 may be greater than 2% by weight.Particles of the chromium-enriched carbide 26 may have a diameter in arange of 5 nm-1.5 μm.

An area of the cross-section or profile 12B proximate and surroundingthe bend radius R is indicated in FIG. 2 as area A1, wherein an areaoutside the area A1, is indicated in FIG. 2 as area A2. Local heating ofthe area A1 proximate the bend radius R during the roll-forming of thecross-section 12B is configured to reduce an amount of thechromium-enriched carbide 26 in the martensitic matrix microstructure 24inside the bend radius R relative to the martensitic matrixmicrostructure outside the bend radius. Specifically, before localheating is applied to area A1 the chromium-enriched carbide 26 ispresent in both areas A1 and A2, and subsequent local heating dissolvesthe carbides in A1. While the reduction of chromium-enriched carbide 26in the bend radius R permits higher ductility for forming, the dispersedchromium-enriched carbide 26 in adjacent area A2 generates increasedstrength and wear resistance of the component 12 outside the bend(s).

As additionally shown in FIG. 2 , the local heating of PHS material inarea A1 during roll-forming permits the radius R to have a relativelysmall magnitude, i.e., the cross-section 12B may have a small ratio ofmaterial thickness t to the bend radius R without cracks or tears havingdeveloped in the bend 22. Specifically, the ratio of material thicknesst to the bend radius R may be 1:1. Typically, the ratio of PHS materialthickness to bend radius in formed parts exceeds 1:1.5 to reduce thelikelihood of cracks and tears. The subject advantageous ratio ofmaterial thickness t to the bend radius R in the cross-section 12Broll-formed from PHS is specifically enabled by enhanced materialformability at higher temperatures, i.e., higher plasticity ofmartensite, enabled by the localized heating described above.

FIG. 5 depicts a method 100 of forming the component 12 from thework-piece blank 10 shown in and described above with respect to FIGS.1-4 . The forming of the component 12 is initiated in frame 102 withproviding a strip of press-hardened steel (PHS). As described above, thework-piece blank 10 may be cut out or blanked from a roll or coil of thePHS. Following frame 102, the method proceeds to frame 104. In frame 104the method includes austenitizing the work-piece blank 10 via heatingthe work-piece blank in the furnace 16 at a predeterminedaustenitization temperature 28, above temperature Ac3, as shown in FIG.6 .

In frame 104 the method further includes soaking the work-piece blank atthe subject predetermined temperature 28 for a predetermined amount oftime 30 (shown in FIG. 6 ) to achieve an austenite microstructure in thecross-section 12B. The predetermined temperature 28 may be in a range of880-950° C. The predetermined amount of soak time 30 may be in a rangeof 1-1000 seconds, and may be further constrained to a range of 200-500seconds. After austenitizing the work-piece blank 10, the methodproceeds to frame 106. In frame 106 the method includes quenching theaustenitized work-piece blank 10 to achieve therein the martensiticmatrix microstructure 24 with dispersed chromium-enriched carbide 26. Asdescribed with respect to FIGS. 1-4 , quenching may be performed at arate greater than 10° C. per second. Specifically, quenching of thework-piece blank 10 may be performed in a salt bath, mixed liquid andair quenching, or via water-cooled die quenching. It is intended for theaustenitized and quenched PHS work-piece blank 10 to have tensilestrength in a range of 1000-2000 MPa.

Following frame 106, the method moves on to frame 108, where the methodincludes roll-forming the austenitized and quenched work-piece blank 10via the system of rolls 18 to generate the cross-section 12B having thebend radius R. After frame 108, the method may proceed to frame 110. Inframe 110 the method includes locally heating the area A1 of the bendradius R during the roll-forming of the cross-section 12B. Local heatingof the area A1 acts to reduce an amount of chromium-enriched carbide inand around the bend radius R relative to the martensitic matrixmicrostructure 24 outside the bend 22 by dissolving thechromium-enriched carbide 26 in the area A1. As described with respectto FIGS. 1-4 , the austenitized and quenched work-piece blank 10 may belocally heated via the heating device 20, for example a laser, amicrowave, or an infrared source.

Following frame 108 or 110, the method may proceed to frame 112. Inframe 112 the method includes cooling the roll-formed component 12, suchas by permitting the component to reach equilibrium with ambienttemperature. Following frame 112, the method may proceed to and concludein frame 114 with trimming excess material, washing, and/or packagingthe final component 12. Generally, the above-disclosed method applied tothe PHS work-piece blank 10, specifically using local heating of theaustenitized and quenched work-piece blank 10 in the area A1 of the bendradius R, is intended to produce a roll-formed component 12 having highstrength, ductility (fracture toughness), and wear resistance inrequisite areas.

The detailed description and the drawings or figures are supportive anddescriptive of the disclosure, but the scope of the disclosure isdefined solely by the claims. While some of the best modes and otherembodiments for carrying out the claimed disclosure have been describedin detail, various alternative designs and embodiments exist forpracticing the disclosure defined in the appended claims. Furthermore,the embodiments shown in the drawings or the characteristics of variousembodiments mentioned in the present description are not necessarily tobe understood as embodiments independent of each other. Rather, it ispossible that each of the characteristics described in one of theexamples of an embodiment can be combined with one or a plurality ofother desired characteristics from other embodiments, resulting in otherembodiments not described in words or by reference to the drawings.Accordingly, such other embodiments fall within the framework of thescope of the appended claims.

What is claimed is:
 1. A method of forming a component having a cross-section having a bend characterized by a bend radius, the method comprising: providing a work-piece blank from press-hardened steel (PHS); austenitizing the work-piece blank in a furnace via heating the work-piece blank to achieve therein an austenite microstructure, including soaking the strip of PHS for a predetermined amount of time; quenching the austenitized work-piece blank to achieve therein a martensitic matrix microstructure with dispersed chromium-enriched carbide; and roll-forming the austenitized and quenched work-piece blank via at least one set of rolls to generate the cross-section having the bend radius.
 2. The method of forming the component of claim 1, locally heating an area of the bend radius during the roll-forming of the cross-section to reduce an amount of chromium-enriched carbide in the martensitic matrix microstructure inside the bend radius relative to the martensitic matrix microstructure outside the bend radius, and thereby generating the component having high strength, ductility, and wear resistance.
 3. The method of forming the component of claim 1, wherein the predetermined amount of time is in a range of 1-1000 seconds.
 4. The method of forming the component of claim 1, wherein the quenching is performed at a rate greater than 10° C. per second.
 5. The method of forming the component of claim 1, wherein the cross-section has a 1:1 ratio of material thickness to the bend radius without cracks or tears.
 6. The method of forming the component of claim 1, wherein locally heating the austenitized and quenched work-piece blank is performed via one of a laser, a microwave, and an infrared device during the roll-forming.
 7. The method of forming the component of claim 1, wherein the PHS of the work-piece blank includes carbon (C) in a range of 0.05-0.45% by weight, manganese (Mn) in a range of 0-4.5% by weight, chromium (Cr) in a range of 0.5-6% by weight, and silicon (Si) in a range of 0.5-2.5% by weight.
 8. The method of forming the component of claim 1, wherein an amount of chromium in the chromium-enriched carbide is greater than 2% by weight, and wherein particles of the chromium-enriched carbide have a diameter in a range of 5 nm-1.5 μm.
 9. The method of forming the component of claim 1, wherein the martensitic matrix microstructure with dispersed chromium-enriched carbide includes: martensite (with optional austenite at less than 10% by volume and optional ferrite at less than 5% by volume) at greater than 85% by volume; and chromium-enriched carbide in a range of 0.2-10% by volume.
 10. The method of forming the component of claim 1, wherein the austenitized and quenched work-piece blank has a tensile strength in a range of 1000-2000 MPa.
 11. A roll-formed high strength, ductility, and wear resistant component comprising: a cross-section having a bend characterized by a bend radius roll-formed from austenitized and quenched work-piece blank from a press-hardened steel (PHS) having a martensitic matrix microstructure with dispersed chromium-enriched carbide; wherein, relative to the martensitic matrix microstructure outside the bend radius, the martensitic matrix microstructure in the bend radius has a reduced amount of the chromium-enriched carbide.
 12. The component of claim 11, wherein the cross-section has a 1:1 ratio of material thickness to the bend radius without cracks or tears.
 13. The component of claim 11, wherein the PHS of the work-piece blank includes carbon (C) in a range of 0.05-0.45% by weight, manganese (Mn) in a range of 0-4.5% by weight, chromium (Cr) in a range of 0.5-6% by weight, and silicon (Si) in a range of 0.5-2.5% by weight.
 14. The component of claim 11, wherein an amount of chromium in the chromium-enriched carbide is greater than 2% by weight.
 15. The component of claim 14, wherein particles of the chromium-enriched carbide have a diameter in a range of 5 nm-1.5 μm.
 16. The component of claim 11, wherein the martensitic matrix microstructure with dispersed carbide includes: martensite (with optional austenite at less than 10% by volume and optional ferrite at less than 5% by volume) at greater than 85% by volume; and chromium-enriched carbide in a range of 0.2-10% by volume.
 17. The component of claim 11, wherein the austenitized and quenched work-piece blank from has a tensile strength in a range of 1000-2000 MPa.
 18. A method of forming a structural component including a cross-section having a bend characterized by a bend radius, the method comprising: providing a work-piece blank from press-hardened steel (PHS) having carbide enriched with an amount of chromium greater than 2% by weight; austenitizing the work-piece blank in a furnace via heating the strip of sheet metal to achieve therein an austenite microstructure, including soaking the work-piece blank for 200-500 seconds; quenching the austenitized work-piece blank at a rate greater than 10° C. per second to achieve therein a martensitic matrix microstructure with dispersed chromium-enriched carbide to achieve ultimate tensile strength thereof in a range of 1000-2000 MPa; roll-forming the austenitized and quenched work-piece blank via at least one set of rolls to generate the cross-section including the bend radius; and locally heating an area of the bend radius during the roll-forming of the cross-section to reduce an amount of the chromium-enriched carbide in the martensitic matrix microstructure inside the bend radius area relative to the martensitic matrix microstructure outside the bend radius, and thereby generating the structural component having high strength, ductility, and wear resistance.
 19. The method of forming the structural component of claim 18, wherein the PHS of the work-piece blank includes carbon (C) in a range of 0.05-0.45% by weight, manganese (Mn) in a range of 0-4.5% by weight, chromium (Cr) in a range of 0.5-6% by weight, and silicon (Si) in a range of 0.5-2.5% by weight.
 20. The method of forming the structural component of claim 18, wherein the martensitic matrix microstructure with dispersed chromium-enriched carbide includes: martensite (with optional austenite at less than 10% by volume and optional ferrite at less than 5% by volume) at greater than 85% by volume; and chromium-enriched carbide in a range of 0.2-10% by volume. 